In semiconductor processing, many operations, such as ion implantation, may be performed on a workpiece or semiconductor wafer. As ion implantation processing technology advances, a variety of ion implantation temperatures at the workpiece can be implemented to achieve various implantation characteristics in the workpiece. For example, in conventional ion implantation processing, three temperature regimes are typically considered: cold implants, where process temperatures at the workpiece are maintained at temperatures below room temperature, hot implants, where process temperatures at the workpiece are maintained at high temperatures typically ranging from 300-600° C., and so-called quasi-room temperature implants, where process temperatures at the workpiece are maintained at temperatures slightly elevated above room temperature, but lower than those used in high temperature implants, with quasi-room temperature implant temperatures typically ranging from 50-100° C.
Hot implants, for example, are becoming more common, whereby the process temperature is typically achieved via a dedicated high temperature electrostatic chuck (ESC), also called a heated chuck. The heated chuck holds or clamps the workpiece to a surface thereof during implantation. A conventional high temperature ESC, for example, comprises a set of heaters embedded under the clamping surface for heating the ESC and workpiece to the process temperature (e.g., 300° C.-600° C.), whereby a gas interface conventionally provides a thermal interface from the clamping surface to the backside of the workpiece. Typically, a high temperature ESC is cooled through radiation of energy to the chamber surfaces in the background.
Chilled ion implantation processes are also common, where conventionally, a room temperature workpiece is placed on a chilled chuck, and the chilled chuck is cooled to a chilled temperature (e.g., a temperature below room temperature), thereby cooling the workpiece. Cooling the chilled chuck provides for a removal of thermal energy imparted into the workpiece from the ion implantation, while further maintaining the chuck and workpiece at the chilled temperature during the implant via the removal of heat through the chilled chuck.
Ion implantation processes are also performed at so-called “quasi-room temperature” (e.g., a temperature slightly elevated above room temperature, such as at 50-60° C., but not as high as a hot ion implantation process), whereby a low-heat chuck (e.g., a chuck configured to heat to a temperature less than 100° C.) has been conventionally used to control the temperature of the workpiece during implantation. However, in the use of such low-heat chucks, a relatively cold (e.g., room temperature, approximately 20° C.) workpiece is placed onto the low-heat chuck, whereby a backside gas thermally couples low-heat chuck and workpiece, thereby transferring energy from the low-heat chuck into the workpiece until an equilibrium temperature is reached prior to conducting the ion implantation.
Such a heating of the workpiece by a low-heat chuck, however, can lead to variations in implant temperature from workpiece to workpiece, as energy is not only transferred from the low-heat chuck to the workpiece prior to implant, but heat is also generated from the implant, itself, whereby the temperature of the low-heat chuck can fluctuate over a period of time. Such fluctuations can have deleterious effects on homogeneity of implants from workpiece to workpiece, and the variations can be exacerbated during startup of the implant system, when a steady-state operation has not yet been reached.
Typically, high temperature ESCs (e.g., heated chucks) are only utilized for hot implants, as they pose a problem if the desired processing is changed from high temperature processing (e.g., 300° C.-600° C.) to a quasi-room temperature processing (e.g., <100° C.) due, at least in part, to the configuration of the heaters therein, and control mechanisms for controlling the temperature of the implant. Thus, when changing from a high temperature implant to a quasi-room temperature implant, the heated chuck would be replaced by a low-heat chuck, whereby the heated chuck and low-heat chuck have differing heat transfer capabilities specifically designed for the desired processing temperature.